BELGRADE (Reuters) -- Serbia's president has promised to protect hundreds of gay and human rights activists on September 20 when they stage the first gay pride parade in the capital since a similar march in 2001 ended in violent clashes.

Ultranationalist groups and hooligans have threatened to attack the march, and police are deploying around 5,000 policemen in central Belgrade and advising participants to stay with the group.

"The state will do everything to protect all its citizens regardless of their religious, sexual, or political affiliation," President Boris Tadic said in a statement.

It will be the first public event staged by lesbian, gay, bisexual and transgender (LGBT) activists since 2001, when dozens of gay activists and policemen were injured in clashes with nationalists, neo-Nazis, and soccer hooligans.

Foreign nongovernment organisations and LGBT groups have called on Tadic and his ruling Democratic Party to lead the fight against all forms of discrimination.

"Given the present context of homophobia, we would like to express the hope that the Democratic Party, the member of our European political family in your country, can become an example of the fight against discriminations," said Rainbow Rose, a European gay-lesbian social-democratic organization.

Despite strong opposition from the church, Serbia adopted a Law against Discrimination earlier this year, the final legal condition Belgrade had to meet to win visa-free travel for its citizens to the European Union in early 2010.

The general population is deeply ambivalent about homosexuality. Thirty-one percent of 4,718 respondents in a 2008 survey believed violence should be used to interrupt LGBT public events. Forty-nine percent were opposed and 20 percent had no opinion.

The September 20 march is seen by some as a test of Serbia's readiness to become a more modern, open society after the fall of communism in the 1990s.

A top church leader earlier this week called the event the "Sodom and Gomorrah on the streets of Belgrade."

Ultranationalist movement "1389" on September 18 made offers to local media to buy photographs of the participants in the rally and post them on a website to help parents "protect their children from sexually deviant persons."

Police said that given the threats, they are treating the march as a "high-risk event."

Trouble Ahead

Calls by the president and the government to refrain from violence meant little to one skinhead group in the drab, communist-era apartment blocks in the New Belgrade neighborhood.

Their leader Pavle, in his 30s, who declined to give his last name in an interview with Reuters, said they "were ready and waiting to show strength."

"This is a Christian country and we will not allow those who oppose the basics of Christianity to demonstrate their wicked and rotten values in public," Pavle said.

His threats, as well as new graffiti on Belgrade walls blaring "Death to Gays," would not deter Milan and Stevan, a gay couple from Belgrade who planned to take part in the rally.

"We will go to protest against discrimination not only of the gay and lesbian population but of all minority groups and we do not fear injuries or even more discrimination," Milan told Reuters.

"As if it isn't enough for us to fight conservative values, we must also stand against freaks who want to beat us over our sexual preferences," added Stevan.

Traditionally conservative and macho-dominated Balkan societies have been slow to adjust to open homosexuality.

In Bosnia, the first gay festival organized in 2008 in Sarajevo was interrupted after hooded men, some shouting Islamic slogans, attacked 250 visitors to opening night.

In Slovenia, following several years of traditional pride parades, a group of masked men attacked and injured a gay activist in June.

Gay visibility in Kosovo has been low and some go to live abroad in search of more open societies, and while there have no reports of violence in Croatia, the police keep a close eye on pride parades.

Albania has never hosted a pride parade but earlier this year the prime minister surprised both the country's conservatives and its gay community by promising to make same-sex marriage legal.